SEWER DESIGN 



CHAPTER I 

 GENERAL CONSIDERATIONS 



IN preparing the design and making the plans for a system 

 of sewers for any given city, there are some preliminary ques- 

 tions to be settled before the location of the mains and the 

 sizes of the pipes can be determined. Perhaps the first of these 

 questions is whether the system shall be designed to carry house- 

 sewage alone, or rain-water from the streets, roofs, and yards 

 as well. Arguments for the one arrangement or the other have 

 been carried on in the abstract for many years, chiefly from 

 the sanitary standpoint, but the question is properly settled by 

 the local conditions of the place under consideration. 



The combined system, as the system intended for rain-water 

 and sewage is called, is the result of growth and development and 

 so has the prestige that comes from age. Not very long ago, 

 the function of sewers was to carry off the storm-water falling on 

 the streets and to keep the yards and basements dry; while 

 the privies, which were then generally used, were cleaned and 

 cared for without reference to the sewers. When water- 

 closets came into use they were, after a time, for it was at 

 first forbidden by law, allowed to discharge into the storm- 

 sewers. In this way the channels, which may have been in the 

 beginning brooks, afterwards walled in and arched over as the 

 city grew, came to be the receptacles for the house-refuse and 

 water-closet wastes. Naturally, the channels thus developed 

 were not of the best section or design for this, their final use, 



